Formation of Terrestrial Planets

The formation of terrestrial planets like Earth, Mars, Venus, and Mercury is a complex process that occurred in the close vicinity of the parent star. These planets formed through a series of stages involving the protoplanetary disk, planetesimals, and accretion.

Protoplanetary Disk:
- The formation of terrestrial planets begins with the protoplanetary disk, a rotating disk of gas and dust that surrounds a young star.
- This disk is composed of mostly hydrogen and helium, along with heavier elements like carbon, oxygen, and iron.
- Over time, the material in the disk begins to clump together due to gravitational forces.

Planetesimals:
- As the material in the protoplanetary disk clumps together, it forms small solid objects called planetesimals.
- These planetesimals are composed of rock, dust, and ice, and range in size from a few meters to several kilometers.
- The planetesimals continue to grow through collisions and accretion of smaller particles.

Accretion:
- Accretion is the process by which planetesimals collide and merge, gradually forming larger bodies.
- As the planetesimals collide, their gravitational forces cause them to stick together, forming protoplanets.
- These protoplanets continue to grow through further accretion of smaller objects, eventually becoming fully formed terrestrial planets.

Proximity to Parent Star:
- The terrestrial planets formed in the close vicinity of the parent star because the protoplanetary disk is denser and warmer closer to the star.
- The higher temperatures in this region allowed for the condensation and solidification of heavier elements like iron and rock.
- In contrast, the outer regions of the protoplanetary disk are colder and composed mainly of gas and ice, which favored the formation of gas giants like Jupiter and Saturn.

Conclusion:
In conclusion, the terrestrial planets were formed in the close vicinity of the parent star, within the denser and warmer inner regions of the protoplanetary disk. The process involved the clumping of material in the disk to form planetesimals, which then underwent accretion to become protoplanets and eventually fully formed terrestrial planets. The proximity to the parent star allowed for the condensation and solidification of heavier elements, leading to the formation of rocky planets like Earth.